Method of coating a substrate with coal acids and article produced thereby



July 4, 1961 H. B. RICKERT 2,991,189 METHOD OF COATING A SUBSTRATE WITHCOAL ACIDS AND ARTICLE PRODUCED THEREBY Filed Jan. 11, 1957 1 N V ENTOR. f/erber/ 5 R/cker/ HTTORA/EYS United States Patent i METHOD OFCOATING A SUBSTRA'IE WITH COAL ACIDS AND ARTICLE PRODUCED 'IHEREBYHerbert B. Rickert, Midland, Micln, assignor to The Dow ChemicalCompany, Midland, Mich., a corporation of Delaware Filed Jan. 11, 1957,Ser. No. 633,695 8 Claims. (Cl. 1 17-6) This invention relates toprotective coated articles or substrates and to their method ofmanufacture. More particularly, it relates to articles or substrateswhich have been coated vw'th a coal acids-base water-soluble protectivecoating which afiords scratch resistance, fire resistance, and non-polarorganic solvent resistance properties to various articles ofmanufacture, which coatings can readily be removed when desired.

Many temporary protective coatings are known. The majority of thosepresently in use lack one or more desirable physical properties, presentdifficulties in their removal, or are relatively expensive.

It has now been discovered that coal acids can be deposited as filmsupon various substrates to provide relatively inexpensive protectionagainst marring, and aifording non-polar organic solvent resistance andfire resistance under conditions where water-solubility is not material.Because of their water-solubility, such films of coal acids are readilyremovable when desired by washing with water.

The coal acids utilized in this invention are advantageously applied asaqueous solutions. It is desirable that the final film contain between0.5 and 10 percent by weight of water as plasticizer to improveflexibility. The water content of coal acids films is readily regulatedby drying at relative humidities ranging between about 20 and 75percent.

The most generally useful coal acids solutions contain about 30 to 85percent by weight of coal acids, solution basis. They can be applied bybrushing, spraying, dipping or equivalent means. Solutions containingbetween 30 and 70 percent coal acids are used for non-porous surfaces orwhere penetration is desired, While solutions containing between 70 and85 percent coal acids are used where very porous surfaces are beingcoated or where a relatively thick film is desired. Room temperaturedrying is generally preferable.

Many types of substrates can be coated to deposit a coal acids film, forexample, paper, wood, glass, metal, plastics, and the like. 7

It is sometimes desirable to include a small amount of a non-ionicwetting agent, for example, 0.2 to percent by weight of coatingcomposition, to facilitate levelling out.

The coal acids that are useful in the compositions of this invention areidentical with or similar to those which are obtained by the oxidationwith gaseous oxygen or air of an aqueous alkaline slurry of a finelydivided carbonaceous material selected from the group consisting of coalor coke that has been obtained by the carbonizzation of coal attemperatures below about 700 C. Coal acids that have been obtained bythe nitric acid oxidation of suitable carbonaceous materials are alsosatisfactory. Such coal varieties as anthracite, bituminous,sub-bituminous and lignite or other low grade coals are suitable for theproduction of coal acids. Satisfactory cokes are those producedaccording to conventional techniques from coal at a temperature belowabout 700 F. The utilization of higher coking temperatures frequentlycauses the cakes that are obtained to be graphitic and Patented July 4,1961 ice rendered unsuitable for conversion to coal acids insatisfactory yields.

The preparation of coal acids from coal may, by way of illustration,involve mixing a ground bituminous coal with a caustic alkali, such assodium hydroxide, and water, using an excess of the caustic with respectto the amount that is contemplated as being required for neutralizingthe coal acids formed. Generally, an apparatus is employed that isconstructed from a corrosion-resisting material of construction and thatis adapted for operation under pressure. The apparatus is also equippedwith an efficient mixing or agitating mechanism and with suitableheat-exchanging means. The weight ratio of the charged ingredients may,for example, be in the proportion of about 3 parts by weight of the coalto 9 parts by weight of the caustic alkali to parts by weight of water.Oxygen is bubbled through the agitated charged ingredients while theyare maintained at a temperature between about 200 and 300 C. and under apressure of from about 500 to 1200 pounds per square inch. Theexothermic reaction is continued until substantially all of thecarbonaceous ingredients of the coal have gone into solution. Thisusually requires a period of time between about 2 and 3 hours. In theoxidation reaction that occurs, about half of the carbon in the coal isconverted to organic acid compounds while the remainder is oxidized tocarbon dioxide. Upon termination of the reaction and cooling of thereaction mass, the coal ash is filtered out of the alkaline solutionthat is obtained.

The coal acids may then be isolated by acidifying the solution with amineral acid, e.g., sulfuric acid and, after filtration, recovering thefree, water-soluble coal acids by extraction with a suitablesolvent,'such as methyl ethyl ketone, which does not dissolve in waterin the presence of such salts as sodium sulfate which are obtained inthe acidified free coal acid solution. Known evaporation and dryingtechniques are employed for subsequently isolating the free coal acids.The coal acids may thus be prepared as solid materials that are oftenpulverized for subsequent handling in a powder form.

The free coal acids product is a hygroscopic, usually yellowish,essentially water soluble material, believed to be comprisedsubstantially of various aromatic polycarboxylic acids. The averagemolecular weight of the coal acids that are ordinarily obtained isusually in the neighborhood of 250. Their average equivalent weight isgenerally about 80. They ordinarily appear to have an average of 2.5 to5 carboxylic groups per molecule with an apparent average of about 3 to4 being common. They evidently contain considerable quantities of triandtetracarboxylic benzene acids as well as aromatic acids having morecomplex nuclei. Frequently, for example, the greatly preponderantproportion of aromatic nuclei obtained in coal acids prepared in thedescribed fashion have been found to consist of methylnaphthalene,benzene, biphenyl, naphthalene, phenanthrene, alkylbenzene, benzophenoneand toluene nuclei.

The single figure-drawing illustrates one of the embodiments of theinvention.

The following examples represent specific embodiments of this invention.

EXAMPLE 1 A 50 percent by weight aqueous solution of coal acids wasbrushed on the surface of a glass plate. Upon evaporation of water atroom temperature at a relative humidity of about 50 percent the driedfilm was clear, strongly adherent and resistant to removal by petroleumether, toluene and methylene chloride. The blue flame from a Bunsenburner caused the film to char but not to flame. Combustion did notcontinue after removal of the Bunsen burner flame. A perspective drawingof a glass plate coated with such a film of coal acids is shown in thefigure.

EXAMPLE 2 A 75 percent by weight aqueous solution of coal acids wasapplied to 40 pound unbleached kraft paper by means of a conventionalnumber 20 Meyer wire rod and dried at room temperature. The dried filmhad a thickness of 0.003 in. Four-inch square test specimens of coatedpaper resisted the passage of turpentine for more than 1800 seconds, asdetermined by the method of ASTM D722-45, modified in that only 4 testspecimens were run and in that two 1 in. square magnesium blocksweighing 55 grams total were placed over the turpentinewetted sand toinsure better contact with the paper. The same paper was coated with a0.002 in. film of 60 percent styrene-4O percent butadiene copolymerlatex and was subjected to the same test. It was penetrated in 600seconds by the turpentine.

EXAMPLE 3 Comparative fiberboard packs were coated to give approximatelythe same film thickness with an aqueous 75 percent by weight coal acidssolution and with percent by weight 15 centipoise methylcellulosesolution. One set of comparative fiberboard packs was filled withstandard petroleum base grease. The other set was filled with S.A.E. 50oil. The time necessary for the grease and the oil to spot the outsideof the fiberboard packs was noted with the following results:

A. Grease screening tests Coating: Spotting time, hours None I 40Methylcellulose 475 Coal acids 620 B. Oil screening tests Coating:Spotting time, hours None 3 Methylcellulose 21 Coal acids 8() EXAMPLE 4A '50 percent solution of coal acids in water was brushed on thefollowing substrates:

.1 in. x 3 in. x /s in. mild steel sheet 1 in. x 3 in. x /8 in.polystyrene sheet /2 in. x 5 in. x A; in. plastic sheet (copolymer of 80percent styrene and 20 percent methacrylic acid) Ms in. x V2 in. x 2 in.plastic sheet (copolymer of 60 percent styrene and 40 percent vinylcyanide) The solutions on all four substrates were dried at 50 percentrelative humidity to give continuous protective films 2 to 4 mils thick.

EXAMPLE 5 EXAMPLE 6 An 85 percent solution of coal acids was applied toa series of three pieces of kraft paper with a No. 20 Meyer Wire rod.The coated papers were placed in saries m humidity chambers maintainedat relative humidities of 20 percent, 51 percent, and 76 percent,respectively. The solutions on all three papers dried to give continuousprotective films 2 mils thick. However, the film dried at 76 percentrelative humidity was somewhat sticky, whereas the other films were tackfree.

What is claimed is:

1. A process for making a coated substrate having a water removableprotective film which comprises depositing upon a substrate a continuousfilm of coal acids, said coal acids being the water-soluble, mixedaromatic carboxylic acids that are the products of the oxidation ofcarbonaceous materials, which acids typically have an average molecularweight of about 250, an average equivalent weight of about 80 andcontain an average of from about 2.5 to 5 carboxylic groups per aromaticnucleus in their molecules.

2. The process of claim 1 wherein the substrate is coated with anaqueous solution of coal acids containing between 30 and weight percentof coal acids, said coal acids being the water-soluble, mixed aromaticcarboxylic acids that are the products of the oxidation of carbonaceousmaterials, which acids typically have an average molecular weight ofabout 250, an average equivalent weight of about 80 and contain anaverage of from about 2.5 to 5 carboxylic groups per aromatic nucleus intheir molecules.

3. A substrate having a continuous water-plastified film of coal acids,said coal acids being the water-soluble, mixed aromatic carboxylic acidsthat are the products of the oxidation of carbonaceous materials, whichacids typically have an average molecular weight of about 250, anaverage equivalent weight of about 80 and contain an average of fromabout 2.5 to 5 carboxylic groups per aromatic nucleus in theirmolecules.

4. Glass having a continuous water-plastified film of coal acids, saidcoal acids being the water-soluble, mixed aromatic carboxylic acids thatare the products of the oxidation of carbonaceous materials, which acidstypically have an average molecular weight of about 250, an averageequivalent weight of about 80 and contain an average of from about 2.5to 5 carboxylic groups per aromatic nucleus in their molecules.

5. Paper having a continuous water-plastified film of coal acids, saidcoal acids being the water-soluble, mixed aromatic carboxylic acids thatare the products of the oxidation of carbonaceous materials, which acidstypically have an average molecular weight of about 250, an averageequivalent weight of about 80 and contain an average of from about 2.5to 5 carboxylic groups per aromatic nucleus in their molecules.

6. Fiberboard having a continuous water-plastified film of coal acids,said coal acids being the water-soluble, mixed aromatic carboxylic acidsthat are the products of the oxidation of carbonaceous materials, whichacids typically have an average molecular weight of about 250, anaverage equivalent weight of about 80 and contain an average of fromabout 2.5 to 5 carboxylic groups per aromatic nucleus in theirmolecules.

7. Polymeric styrene having a continuous water-plastified film of coalacids, said coal acids being the watersoluble, mixed aromatic carboxylicacids that are the products of the oxidation of carbonaceous materials,which acids typically have an average molecular weight of about 250, anaverage equivalent weight of about 80 and contain an average of fromabout 2.5 to 5 carboxylic groups per aromatic nucleus in theirmolecules.

8. Mild steel having a continuous water-plastificd film of coal acids,said coal acids being the water-soluble, mixed aromatic carboxylic acidsthat are the products of the oxidation of carbonaceous materials, whichacids typically have an average molecular weight of about 250, anaverage equivalent weight of about 80 and contain an average of fromabout 2.5 to 5 carboxylic groups per aromatic nucleus in theirmolecules.

References Cited in the file of this patent UNITED STATES PATENTS 5Tsheppe Feb. 5, 1889 Jacobsohn Sept. 21, 1937 Izard June 13, 1939Juettner Oct. 17, 1939 10 6 Grosskinsky et a1. Mar, 12, 1957 Goren Mar.19, 1957 Rickert et-al. Mar. 11, 1958 Bozer et a1. Feb. 24, 1959 RickertMar. 22, 1960 FOREIGN PATENTS Great Britain May 2, 1951 Great BritainMar. 14, 1956

1. A PROCESS FOR MAKING A COATED SUBSTRATE HAVING A WATER REMOVABLEPROTECTIVE FILM WHICH COMPRISES DEPOSITING UPON A SUBSTRATE A CONTINUOUSFILM OF COAL ACIDS, SAID COAL ACIDS BEING THE WATER-SOLUBLE, MIXEDAROMATIC CARBOXYLIC ACIDS THAT ARE THE PRODUCTS OF THE OXIDATION OFCARBONACEOUS MATERIALS, WHICH ACIDS TYPICALLY HAVE AN AVERAGE MOLECULARWEIGHT OF ABOUT 250, AN AVERAGE EQUIVALENT WEIGHT OF ABOUT 80 ANDCONTAIN AN AVERAGE OF FROM ABOUT 2.5 TO 5 CARBOXYLIC GROUPS PER AROMATICNUCLEUS IN THEIR MOLECULES.